Japanese citizens Makoto Kobayashi, left, and Toshihide Masukawa, centre, and Japanese-born American Yoichiro Nambu, shown in these undated photos, won the 2008 Nobel Prize in Physics for discoveries in the world of subatomic physics, the Royal Swedish Academy of Sciences announced Tuesday.

Two Japanese citizens and an American born in Japan won the 2008 Nobel Prize in Physics on Tuesday for their work in the world of subatomic physics.

The Nobel committee for physics at Royal Swedish Academy of Sciences said the prize is shared by:

• Japanese-born Yoichiro Nambu of the University of Chicago for his discovery of a mechanism called spontaneous broken symmetry in subatomic physics.
• Makoto Kobayashi and Toshihide Maskawa for their discovery of the origin of broken symmetry that predicts the existence of at least three families of quarks in nature.

"Spontaneous broken symmetry conceals nature's order under an apparently jumbled surface," the academy said in its citation.

"Nambu's theories permeate the standard model of elementary particle physics. The model unifies the smallest building blocks of all matter and three of nature's four forces in one single theory."

Kobayashi and Maskawa "explained broken symmetry within the framework of the standard model but required that the model be extended to three families of quarks."

The three scientists will share $1.4 million US, a diploma and an invitation to the prize ceremonies in Stockholm on Dec. 10.

It's the second Nobel award to be announced this week. The honour for medicine was announced on Monday.

Sweden's Alfred Nobel, who was credited with inventing dynamite, created the prizes in his will in the areas of medicine, physics, chemistry, literature and peace. The economics prize was created by Sweden's central bank in 1968.